[Test-Equipment] Millen GDO question

Sun Jul 31 21:15:06 EDT 2011

That's good to know as I was not aware that they went up that high.  Do you
have any links to sources?

Randy, KI6WAS

-----Original Message-----
From: test-equipment-bounces at mailman.qth.net
[mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Carl
Sent: Sunday, July 31, 2011 4:17 PM
To: Discussion of Electronic Test Equipment
Subject: Re: [Test-Equipment] Millen GDO question

Thats ancient history. They now have HV film resistors the size of a 1W 
carbon good for 5KV and others much higher. They are not that expensive 
either, I use them in ham amps as the string to the voltmeter.

Carl
KM1H

----- Original Message ----- 
From: "Randy D. Hunt" <randy_hunt960 at yahoo.com>
To: "'Discussion of Electronic Test Equipment'" 
<test-equipment at mailman.qth.net>
Sent: Sunday, July 31, 2011 6:45 PM
Subject: Re: [Test-Equipment] Millen GDO question

> Carbon Comps have another advantage - higher voltage rating.  That's why 
> you
> find them in voltage divider strings in things like "scopes". . .
>
>
> Randy
> -----Original Message-----
> From: test-equipment-bounces at mailman.qth.net
> [mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Fuqua, Bill L
> Sent: Sunday, July 31, 2011 12:01 PM
> To: Richard Knoppow; Discussion of Electronic Test Equipment; Mike Manes
> Subject: Re: [Test-Equipment] Millen GDO question
>
> Not that this has much to do with this issue but some components values
> change over 50 or more years.
>
> From: test-equipment-bounces at mailman.qth.net
> [test-equipment-bounces at mailman.qth.net] On Behalf Of Richard Knoppow
> [1oldlens1 at ix.netcom.com]
> Sent: Sunday, July 31, 2011 10:38 AM
> To: Mike Manes; Discussion of Electronic Test Equipment
> Subject: Re: [Test-Equipment] Millen GDO question
>
> Carbon composition resistors are very bad. In our stock room we had some
> carbon comp resistors that
> were not only out of tolerance but were up to the next 10% value and they
> were only 10 years old!
> The upper values were the worst. The 1 Meg and above were way off and had
> increased in value 50% or more
> in some cases. Under use they can change value even more.
>  Much of the stuff made in WWII or soon after may have resistors may be 
> way
> off value.
> I wonder if some of the resistors that were treated or coated retained 
> their
> value better than the non-coated ones.
> It seems to me that the oil component of the carbon comp dries up, you can
> see if apply several time its rated
> power. It will sweat or bubble oil onto the surface. And after the test 
> its
> value will be somewhat greater.
> We replace all our carbon comp resistors with carbon films. The carbon 
> comps
> had several advantages but
> we just could not let them die while sitting in the stock room. Now they 
> are
> very hard to get.
> The carbon film resistors can burn out without any outward sign of damage
> and if the epoxy coating is damaged
> they can easily short out.
>   We got some Tektronix 2200 series scopes that started having focus
> problems not long after receiving them
> Discovered a long voltage divider string on the HV supply had carbon comp
> resistors.  They possibly used them
> because they could be put next to the circuit board without worry of 
> arcing.
> But, they increased in value and
> the scopes failed. We replaced them with carbon film resistors and placed
> them about a 1/4 inch above the PCB.
> Since these were in instructional labs we could not wait forTektronix to
> repair them under warranty.
>
> 73
> Bill wa4lav
>
>
> ----- Original Message -----
> From: "Mike Manes" <mrmanes at gmail.com>
> To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>; "Discussion
> of Electronic Test Equipment"
> <test-equipment at mailman.qth.net>
> Sent: Saturday, July 30, 2011 8:37 PM
> Subject: Re: [Test-Equipment] Millen GDO question
>
>
>> Hi Richard,
>>
>> That's pretty characteristic of every GDO I've used,
>> including the
>> Millen, a Knightkit and a really nice piece of homebrew
>> work. I
>> think it has to do with the low VHF Q of the air variable
>> cap that's
>> necessary to get a decent L/C ratio and tuning range on
>> the HF
>> bands.  I've seen GDOs that are specifically designed for
>> VHF and
>> UHF, and tho I haven't used one, I'd expect them to
>> overcome that
>> problem.
>>
>> 73 de Mike W5VSI
>>
>   Thanks Mike, that's what I wanted to know. I think mine
> is working as it should. The low limit of the coil is given
> as 140mhz. The dial is calibrated down to 125mhz. The grid
> current shows some indication down to maybe 130mhz. So, it
> covers the range specified, just not the complete range
> shown on the dial. The next lowest range goes up high enough
> to provide some overlap.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
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